had some guys from southwest research tell me that with synthetics there is almost no difference, but with dino there is plenty and in their research castrol gtx faired the best. pennzoil was at the bottom of the spectrum, valvoline was near the top.
I also use wix filters, if you perfer NAPA or something, they are the same. Napa Gold=WIX. Oreillys sales wix, i dont know who else does.